linux-kernel - Re: [PATCH 16/27] acpi: Disable ACPI table override if the kernel is locked down

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Message-ID: <20171020064612.GX3285@linux-l9pv.suse>
Date:   Fri, 20 Oct 2017 14:46:12 +0800
From:   joeyli <jlee@...e.com>
To:     David Howells <dhowells@...hat.com>
Cc:     linux-security-module@...r.kernel.org, gnomes@...rguk.ukuu.org.uk,
        linux-efi@...r.kernel.org, matthew.garrett@...ula.com,
        gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org,
        jforbes@...hat.com
Subject: Re: [PATCH 16/27] acpi: Disable ACPI table override if the kernel is
 locked down

On Thu, Oct 19, 2017 at 03:52:34PM +0100, David Howells wrote:
> From: Linn Crosetto <linn@....com>
> 
> >From the kernel documentation (initrd_table_override.txt):
> 
>   If the ACPI_INITRD_TABLE_OVERRIDE compile option is true, it is possible
>   to override nearly any ACPI table provided by the BIOS with an
>   instrumented, modified one.
> 
> When securelevel is set, the kernel should disallow any unauthenticated
> changes to kernel space.  ACPI tables contain code invoked by the kernel,
> so do not allow ACPI tables to be overridden if the kernel is locked down.
> 
> Signed-off-by: Linn Crosetto <linn@....com>
> Signed-off-by: David Howells <dhowells@...hat.com>

I have reviewed this patch. Please feel free to add:

Reviewed-by: "Lee, Chun-Yi" <jlee@...e.com>

Thanks!
Joey Lee

> cc: linux-acpi@...r.kernel.org
> ---
> 
>  drivers/acpi/tables.c |    5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/drivers/acpi/tables.c b/drivers/acpi/tables.c
> index 80ce2a7d224b..5cc13c42daf9 100644
> --- a/drivers/acpi/tables.c
> +++ b/drivers/acpi/tables.c
> @@ -526,6 +526,11 @@ void __init acpi_table_upgrade(void)
>  	if (table_nr == 0)
>  		return;
>  
> +	if (kernel_is_locked_down("ACPI table override")) {
> +		pr_notice("kernel is locked down, ignoring table override\n");
> +		return;
> +	}
> +
>  	acpi_tables_addr =
>  		memblock_find_in_range(0, ACPI_TABLE_UPGRADE_MAX_PHYS,
>  				       all_tables_size, PAGE_SIZE);
> 
> --
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